Modeling network

Model Networks. Constmction of model networks allows development of quantitative stmcture property relationships and provide the abiUty to test the accuracy of the theories of mbber elasticity (251—254). By definition, model networks have controlled molecular weight between cross-links, controlled cross-link functionahty, and controlled molecular weight distribution of cross-linked chains. Sihcones cross-linked by either condensation or addition reactions are ideally suited for these studies because all of the above parameters can be controlled. A typical condensation-cure model network consists of an a, CO-polydimethylsiloxanediol, tetraethoxysilane (or alkyltrimethoxysilane), and a tin-cure catalyst (255). A typical addition-cure model is composed of a, ffl-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

The purpose of this review is to show how anionic polymerization techniques have successfully contributed to the synthesis of a great variety of tailor-made polymer species Homopolymers of controlled molecular weight, co-functional polymers including macromonomers, cyclic macromolecules, star-shaped polymers and model networks, block copolymers and graft copolymers. 

Microstructure (see also Stereochemistry and Tacticity) 114,115.128.138,139 Miscibility (see also Compatibility) 12, 53, 68 Model networks 163 Modification of a polymer, chemical 154 Mold release 71, 74 Molecular weight, control 147. 154... 

The effect of restricted junction fluctuations on S(x) is to change the scattering function monotonically from that exhibited by a phantom network to that of the fixed junction model. Network unfolding produces the reverse trend, the change of S(x) with x is even less than that exhibited by a phantom network. Figure 6 illustrates how the scattering function is modified by these two opposing influences. 

Parallel to the development of the new theoretical approaches considerable experimental work was done on model networks especially synthesized, to show the effects of pendent chains, loops, distribution of chain length, functionality of crosslinks, etc. on properties (5-21). In some instances, the properties turned out... 

Until recently ( 1 5 ) investigations utilizing model networks had been limited to functionalities of four or less. Networks with higher functionality are predicted by the various theories of rubber elasticity to display unique equilibrium tensile behavior. As such, these multifunctional networks provide insight into the controversy surrounding these theories. The present study addresses the synthesis and equilibrium tensile behavior of endlinked model multifunctional poly(diraethylsilox-ane) (PDMS) networks. 

As is clear from the earlier discussions of pre-gel intramolecular reaction, such reaction in principle always occurs in random polymerisations, although its amount may be reduced by using reactants of higher molar mass, lower functionalities, and stiffer chain structures. Thus, the use of end-linking reactions to produce model networks (for example(35) and references quoted... 

Model networks were prepared using hydroxyl terminated polymer and isocyanates, (a) Bifunctional hydroxyl terminated polybutadiene (Butarez, from Phillips Petroleum) was crosslinkined with tris (p-isocyanatophenyl)-thiophosphate (Desmodur RF, from Mobay Chemical Co.). This crosslinked... 

We appreciate the guidance of Pro . R.W. Lenz in the synthesis of model networks, and the help of Drs. Roberto Russo and Ulku Yilmazer in initial synthesis work. This work was supported in part by a grant from the Center for University of Massachusetts-lndustry Research on Polymers (CUMIRP). We appreciate the donation of the Duragen samples by the General Tire and Rubber Co., the isocyanate samples by the Mobay Chemical Co., and the Butarez samples by the Phillips Petroleum Co. 

Monocyclopentadienyl compounds, 25 116 Monodentate chelants, 5 709 Monodentate ligands, 9 396 Monodisperse model networks, with silicone, 22 570... 

See also Biodegradable polymer networks Filled silicone networks Interpenetrating networks (IPNs) Model silicone networks Monodisperse model networks ... 

Tensile modulus (Young s modulus), 20 177, 29 743, 20 346 monodisperse model networks and, 22 570... 

A. Ciliberto, F. Capuani, and J. J. Tyson2, Modeling networks of coupled enzymatic reactions using the total quasi steady state approximation. PLoS Comput. Biol. 3(3), e45 (2007). 

Note 1 A model network can be prepared using a non-linear polymerization or by crosslinking of existing polymer chains. 

Note 2 A model network is not necessarily a perfect network. If a non-linear polymerization is used to prepare the network, non-stoichiometric amounts of reactants or incomplete reaction can lead to network containing loose ends. If the crosslinking of existing polymer chains is used to prepare the network, then two loose ends per existing polymer chain result. In the absence of chain entanglements, loose ends can never be elastically active network chains. 

Note 3 In addition to loose ends, model networks usually contain ring structures as network imperfections. 

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